The invention concerns a method in a suction dryer which comprises a basin for the suspension to be suction-dried, in connection with which basin one or several disc-shaped components revolve, which consist of filter plates, onto the faces of which a filtrate cake is gathered and dewatered by the effect of a suction flow passing through the filter plates, the filtrate cake/cakes being scraped or otherwise detached from the face or faces of the filter plates.
In the prior art, various suction dryers are known which comprise filter discs composed of finely porous filter plates. The discs are rotated in the suspension to be dewatered, and by the effect of suction, a filtered cake is gathered on the plane faces of the filter plates, which cake is scraped off the faces of the filter plates.
With respect to recent developments of the suction dryers concerned, reference is made to the applicant's earlier Finnish Patent Applications Nos. 870706, 870707, and 871312, reference being made to the constructional details described in the applications.
The usually ceramic filter plates have a tendency to be blocked, because their pore structure is successively filled with finely divided material. In a way known in prior art, attempts have been made to clean the filter plates by passing cleaning liquid through the same in the direction opposite to the circulation of the liquid to be removed, said cleaning liquid usually consisting of water. Moreover, various brush devices have been used for outside cleaning of filter plates.
However, with these prior-art methods and devices, it has not been possible to retain the permeability of the filter plates for a sufficiently long period of time. Instead it has been necessary to replace the filter plates unnecessarily frequently, in relation to their durability in other respects, which increases the filter costs substantially and causes standstills in the process.